ZABBIX
Zabbix is the ultimate enterprise-level software designed for monitoring availability and performance of IT infrastructure components. Zabbix is open source and comes at no cost.
With Zabbix it is possible to gather virtually limitless types of data from the network. High performance real-time monitoring means that tens of thousands of servers, virtual machines and network devices can be monitored simultaneously. Along with storing the data, visualization features are available (overviews, maps, graphs, screens, etc), as well as very flexible ways of analyzing the data for the purpose of alerting.
Thresholds of acceptable limits for incoming data can be set. As soon as those thresholds are surpassed, Zabbix can deliver e-mail notifications informing network administrators about the current or a potential problem.
Zabbix offers great performance for data gathering and can be scaled to very large environments. Distributed monitoring options are available with the use of Zabbix proxies. Zabbix comes with a web-based interface, secure user authentication and a flexible user permission schema. Polling and trapping is supported, with native high performance agents gathering data from virtually any popular operating system; agent-less monitoring methods are available as well.
Web monitoring as well as monitoring of WMware virtual machines is possible with Zabbix. Zabbix can automatically discover network servers and devices, as well as perform low-level discovery with methods of automatically assigning performance and availability checks to discovered entities.
Observium
Observium is an autodiscovering SNMP based network monitoring platform written in PHP which includes support for a wide range of network hardware and operating systems including Cisco, Windows, Linux, HP, Dell, FreeBSD, Juniper, Brocade, Netscaler, NetApp and many more.
Observium has grown out of a lack of network monitoring platforms which are both simple to manage and pleasant to use. It is intended to provide a navigable interface to the health and performance of your network. Its design goals include collecting as much historical data about devices as possible, using as much auto-discovery as possible with little or no manual intervention, and having a very intuitive interface.
Observium is not intended to replace an up/down alerting system like Icinga or Nagios, but rather to complement it with an easy to manage, intuitive representation of historical and current performance statistics, configuration visualisation and syslog capture.
http://www.observium.org/wiki/Main_Page
ZENOSS
Zenoss Core is award-winning Open Source IT monitoring software that offers visibility over the entire IT stack, from network devices to applications. Features include automatic discovery, inventory via CMDB, availability monitoring, easy-to-read performance graphs, sophisticated alerting, an easy-to-use web portal, and much, much more. It is Free Software, released under the GNU General Public License version 2. Zenoss has a very active